1. Field of the Invention
The present invention relates to a headret provided in an automotive seat, and in particular to an arrangement of a movable headrest in the seat, the headrest being of the type displaceable from an upright use position on the seat down to a non-use position below a vision field of an occupant on another seat, so that forward view or backward view can be attained widely from a person on a rear seat or a driver on a front seat, respectively.
2. Description of Prior Art
There has been known a movable headrest of this type displaceable between its erecting use position and lowered non-use position, by which an occupant's head may be normally supported at the use position and otherwise the headrest per se may be moved down to the non-use position for avoiding hindrance to a vision field of another occupant on another seat.
Such headrest, conventionally, has been coupled to a drive mechanism via a one link within a seat, which is typically known from U.S. patent application No. 686,189 assigned to the same assignee of the present invention. According thereto, a pair of stays of headrest are secured on a rotatable shaft disposed within a seat back, and a connecting rod is at its one end connected pivotally to a link piece extending orthogonally from the rotatable shaft. Another end of the connecting rod is formed with a rack gear part which is in mesh with a pinion of a drive mechanism including a motor. Actuating the motor causes the connecting rod to move vertically through the pinion-and-rack gear transmission, which in turn causes the link piece to rotate simultaneously likewse about the axis of the rotatable shaft. Then the shaft is rotated to displace the headrest between the use and non-use positions. This permits for controlling the motion of headrest and adjusting its deisred positions between the use and non-use positions.
In this sort of headrest construction, as can be seen from the U.S. patent application No. 686,189, typically, the drive mechanism and connecting rod are disposed adjacent to one of both lateral sides of seat back, and as such, no control mechanism is provided at another opposite side of seat back, which means that the control drive force is only imparted to one lateral side of the rotatable shaft connected to the hearest body. Such one-side control or what can be described as cantilever-like transmission has been found defective in that (i) a sudden great load applied to the headrest in a collision case is too intesively exerted on a free side of rotatable shaft which is relatively weak as opposed to the foregoing control side of same shaft to which the connecting rod is connected, thus raising a high likelihood of the shaft being twisted and deformed, in which case, the headrest is also twisted, impairing the appearance of seat, and (ii) a slightly loosen engagement between the pinion and rack gears, which is needed in design for absorbing a variation in angle of mesh between them during vertical translation of the connecting rod, will easily tend to create a slight wobbling in the two gears and such wobbling will be transmitted, when the headrest is at the non-use position, to the headrest body, with an amplified magnitude, through the connecting rod, link piece and shaft which form a leverage serving to transform the slight wobbling into a corresponding larger rotative motions of the stays relative to the shaft forming a fulcrum, thus wobbling the headrest with an unpleasant contact noise, which may give an unstable psychological state to an occupant on the seat, dispersing his or her concentration for driving the car.